Loss of motor function in the lower limbs following spinal cord injury (SCI) results in a rapid reduction in bone mineral density (BMD), especially in trabecular regions, and a subsequent 5 to 23 fold increase in fracture risk. While BMD is currently the best in vivo surrogate for fracture risk widely available, knowledge of trabecular bone microarchitecture could explain substantial overlap in BMD observed in those who do and do not experience skeletal fracture. The PIs hypothesize that within one year of SCI trabecular bone microarchitecture will be impaired in the distal femur and proximal tibia - two common fracture sites. Irrespective of changes in trabecular bone microarchitecture, interventions that prevent rapid bone loss and reduce fracture incidence are needed. Because of the coordinating actions of skeletal muscle and bone, activities that promote skeletal muscle hypertrophy likely promote bone gain. This notion is supported by studies that demonstrate concomitant gains in muscle and bone following resistance training in able-bodied individuals. In clinically complete SCI patients, it has been recently shown that 8 weeks of electromyostimulation (EMS), which evoked high force contractions (simulatating resistance training), reversed the marked decrement of lower limb muscle evident 46 weeks after injury. Whether or not this novel application of EMS can also halt or reverse SCI-induced bone loss has not been determined. The PIs hypothesize that EMS evoked dynamic knee extension exercise will halt deterioration of trabecular bone microarchitecture and increase BMD, bone mineral content (BMC) and muscle mass in the lower limbs after SCI. To test these hypotheses, clinically complete SCI patients will be studied for 6 months starting 3 to 5 months after injury . The Specific Aims of this project are: 1) to determine if trabecular bone microarchitecture is compromised in the distal femur and proximal tibia after SCI; and 2) to determine if EMS evoked knee extension exercise has a positive impact on trabecular bone microarchitecture, BMD, BMC and muscle mass in the lower limbs after SCI. The significance of this research is that it will increase our current understanding of bone biology and potentially result in a novel application of EMS to control bone and muscle loss after SCI, both important secondary complications after injury.